Dual wiper plug system

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed herein generally relate to a downhole wiper plug system and a method of using the downhole wiper plug system. Specifically, embodiments disclosed herein relate to a system of liner wiper plugs used to isolate cement from drilling fluids when pumping cement into the formation. More specifically, embodiments disclosed herein relate to a dual wiper plug system and method of cementing a liner in a borehole using the dual wiper plug system.

2. Background Art

After a borehole has been drilled into the earth, a string of steel casing or liner is lowered and set therein. One drillable shoe and possibly one drillable collar having an upwardly closing check valve are mounted on or near the lower end of the string to prevent back flow. After the liner has been suspended by a hanger apparatus near the lower end of a previously run casing string, cement slurry is pumped down the interior thereof and out into the borehole via the check valves where it flows up in the annulus outside the liner up to a desired level. The drilling mud that was standing in the well prior to cementing is displaced and circulated out of the well during the casing setting and cementing steps. When the cement has hardened, it seals off the annular space between the outside of the liner and the surrounding well bore wall and prevents migration of formation fluids therealong.

It is desirable to protect the cement slurry from contamination by the drilling mud as the slurry is being pumped into the well. The usual practice to protect the cement slurry is to place a first plug ahead of the cement column which provides a separation between the lower end of such column and the mud, and to place a second plug which performs the same function at the top of the column. Each plug typically has a series of upwardly facing elastomer cups whose outer edges engage the inner walls of the liner to provide sliding seals and wipers. When the first plug lands against a float shoe at the bottom of the liner, a passage is opened up through the float shoe which enables cement to be pumped into the annulus. Eventually the second plug lands against the first plug as the displacement is completed. The check valves in the float shoes prevent back flow of the cement into the casing or liner during the time that it takes for the cement to set up. During downward movement, the outer edges of the cups of the second plug wipe or scrape the cement off of the inner walls of the liner so that no deposits are left. Once the cement has hardened, the plugs and cement shoes can be drilled out.

Wiper plugs used in cementing liners have been designed such that cement slurry and other fluids could be pumped through a flow passage in the plug itself, which requires complicated valve systems to open and close this passage. This complexity has resulted in plug structures that may be difficult to drill out at the end of the cementing operation. The inclusion of such valve structures also has reduced the performance characteristics of such plugs, particularly when the liner hanger and wiper plug launching system are used on directional or horizontal sections of a well.

In conventional wiper plug systems, the first and second plugs are engaged with the liner with shear screws. When a predetermined pressure is applied to the first or second plug, the shear screws break and allow the first and/or second plug to continue downward within the liner. Such shear mechanisms may be prose to prematurely releasing (i.e., breaking) if the tool is impacted when run into the hole. If the first plug is prematurely released, the plug may not properly move along the liner or properly seat in a seat of the float shoe. Moreover, if the first plug improperly impacts or lands in the seat, the seat may be damaged or debris may block the check valve.

Accordingly, there exists a need for an efficient and reliable liner wiper system.

SUMMARY OF INVENTION

In one aspect, the embodiments disclosed herein relate to a dual wiper plug system having a first wiper including a first body having a first bore therethrough, and at least one wiper fin disposed around the body, a second wiper disposed axially above the first wiper, the second wiper including a second body having a second bore therethrough and a first shoulder formed on the inner surface of the second body, and at least one wiper fin disposed around the body, and a first collet ring coupled to the first wiper and including at least one collet finger extending axially upward, and a collet head disposed on an upper end of the collet finger and configured to engage the first shoulder of the second body.

In another aspect, embodiments disclosed herein relate to a method of using a dual wiper plug system, the method including running the dual wiper plug system coupled to a running tool into a well, the dual wiper plug system having a first wiper coupled to a second wiper with a first collet device, and a second wiper coupled to the running tool with a second collet device, securing the dual wiper plug system proximate an upper end of a liner, dropping a first pump down plug into the dual wiper plug system, decoupling the first wiper from the second wiper comprising disengaging the first collet device, dropping a second pump down plug into the dual wiper plug system, and decoupling the second wiper from the running tool comprising disengaging the second collet device.

In another aspect, embodiments disclosed herein relate to a landing collar including a housing, a first sleeve configured to receive a lead wiper plug, wherein the first sleeve comprises at least one bypass port, and at least one latching mechanism configured to couple the first sleeve to an inner wall of the housing, wherein the at least one latching mechanism comprises a c-ring coupled to the housing and a landing insert disposed within the c-ring.

Other aspects and advantages of the invention will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

<figref idref="DRAWINGS">FIG. 1A</figref> is a cross-sectional view of a dual wiper plug system in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 1B</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 1A</figref> with a first pump down plug in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 1C</figref> is a cross-sectional view of a lead wiper released from the dual wiper plug system of <figref idref="DRAWINGS">FIG. 1A</figref> in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 1D</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 1A</figref> with a second pump down plug in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 1E</figref> is a cross-sectional view of a follow wiper released from the dual wiper plug system of <figref idref="DRAWINGS">FIG. 1A</figref> in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2A</figref> is a cross-sectional view of a dual wiper plug system in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2B</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 2A</figref> with a first pump down plug in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2C</figref> is a cross-sectional view of a lead wiper released from the dual wiper plug system of <figref idref="DRAWINGS">FIG. 2A</figref> in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2D</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 2A</figref> after a lead wiper has been released in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2E</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 2A</figref> with a second pump down plug in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 2F</figref> is a cross-sectional view of a follow wiper released from the dual wiper plug system of <figref idref="DRAWINGS">FIG. 2A</figref> in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 3</figref> is a cross-sectional view of a dual wiper plug system with a second pump down plug prematurely dropped therein in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 4</figref> is a cross-sectional view of a follow wiper in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 5</figref> is a cross-sectional view of a lead wiper landed in a landing collar disposed below a liner in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 6</figref> is a cross-sectional view of a follow wiper and a lead wiper landed in a landing collar below a liner in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 7A</figref> is a cross-sectional view of a dual wiper plug system in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 7B</figref> is a cross-sectional view of the dual wiper plug system of <figref idref="DRAWINGS">FIG. 7A</figref> with a first pump down plug in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 7C</figref> is a cross-sectional view of a follow wiper released from the dual wiper plug system of <figref idref="DRAWINGS">FIG. 7A</figref> in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 8</figref> is a cross-sectional view of a dual wiper plug system having a second pump down plug stuck therein in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIGS. 9A-9C</figref> show a perspective view and partial cross-section views with an open port position and a closed port position.

<figref idref="DRAWINGS">FIG. 10</figref> is a cross-sectional view of a landing collar disposed below a liner in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 11</figref> is a cross-sectional view of a lead wiper and a follow wiper landed in a landing collar below a liner in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIG. 12</figref> is a cross-sectional view of a component of the landing collar of <figref idref="DRAWINGS">FIGS. 10 and 11</figref>.

<figref idref="DRAWINGS">FIG. 13</figref> is a stage cementing tool in accordance with embodiments disclosed herein.

<figref idref="DRAWINGS">FIGS. 14A and 14B</figref> are cross-sectional views of a dual wiper plug system in accordance with embodiments disclosed herein.

DETAILED DESCRIPTION

Embodiments disclosed herein generally relate to a downhole wiper plug system and a method of using the downhole wiper plug system. Specifically, embodiments disclosed herein relate to a system of liner wiper plugs used to isolate cement from drilling fluids when pumping cement into the formation. More specifically, embodiments disclosed herein relate to a dual wiper plug system and method of cementing a liner in a borehole using the dual wiper plug system.

A liner wiper plug system in accordance with embodiments of the present disclosure is used to isolate cement from drilling fluids when cement is pumped into the formation through the drill string to cement a liner in place. A dual wiper plug system in accordance with embodiments disclosed herein has a first or lead wiper and a second or follow wiper. The lead wiper moves down the drill string in front of a volume of cement to prevent the cement from being contaminated by the drilling fluid. The follow wiper moves down the drill string behind the volume of cement to remove any excess cement from the inner wall of the liner and to provide a barrier between the cement and drill string fluid, thereby preventing contamination of the cement and/or drilling fluid.

Referring initially to <figref idref="DRAWINGS">FIG. 1A</figref>, a dual wiper plug system <b>100</b> in accordance with embodiments disclosed herein is shown. The dual wiper plug system <b>100</b> includes a lead wiper <b>102</b> and a follow wiper <b>104</b>. Each of the lead wiper <b>102</b> and the follow wiper <b>104</b> include one or more wiping fins <b>106</b> disposed circumferentially around the body of the wiper <b>102</b>, <b>104</b> and extending radially therefrom to contact and seal against an inner wall of a liner (not shown). The wiping fins <b>106</b> may be formed from an elastomeric material or any other know material in the art such that the wiping fins <b>106</b> are configured to flex or compress as the wiper <b>102</b>, <b>104</b> is run through a liner or other tubular component having an inside diameter smaller than a maximum diameter of the wiping fins <b>106</b> in an expanded state.

The lead wiper <b>102</b> includes a tubular body <b>108</b> and a nose <b>110</b> disposed on a lower end of the body <b>108</b>. The one or more wiping fins <b>106</b><i>a </i>are coupled to the body <b>108</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. The nose <b>110</b> includes one or more ports <b>112</b> to allow fluid flow from inside the body <b>108</b> to outside the body <b>108</b>. The body <b>108</b> includes a bore <b>116</b> therethrough having a first diameter D<b>1</b><i>a </i>and a second diameter D<b>2</b><i>a</i>, such that the first diameter D<b>1</b><i>a </i>is smaller than the second diameter D<b>2</b><i>a</i>. As shown in <figref idref="DRAWINGS">FIG. 1A</figref>, the first diameter D<b>1</b><i>a </i>of the bore is positioned axially below the second diameter D<b>2</b><i>a</i>, thereby forming a shoulder <b>118</b>. The inside surface of the body <b>108</b> includes a threaded portion <b>114</b>. In one embodiment, the threaded portion <b>114</b> may be disposed proximate the upper end of the lead wiper <b>102</b>, but in other embodiments, the threaded portion <b>114</b> may be disposed proximate the middle or lower end of the lead wiper <b>102</b>. As shown, the threaded portion <b>114</b> may be formed in the first diameter D<b>1</b><i>a </i>of the body <b>108</b>. In one embodiment, the threaded portion <b>114</b> may be a ratchet thread.

The follow wiper <b>104</b> includes a tubular body <b>120</b> and a landing nose <b>122</b> disposed on a lower end of the tubular body <b>120</b>. The one or more wiping fins <b>106</b><i>b </i>are coupled to the body <b>120</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. The body <b>120</b> of the follow wiper <b>104</b> includes a bore <b>124</b> therethrough having a first diameter D<b>1</b><i>b </i>and a second diameter D<b>2</b><i>b</i>, such that the first diameter D<b>1</b><i>b </i>is smaller than the second diameter D<b>2</b><i>b</i>. As shown in <figref idref="DRAWINGS">FIG. 1A</figref>, the first diameter D<b>1</b><i>b </i>of the bore is positioned axially below the second diameter D<b>2</b><i>b</i>, thereby forming a shoulder <b>126</b>. The first diameter D<b>1</b><i>b </i>of the follow wiper <b>104</b> may be larger than the first diameter D<b>1</b><i>a </i>of the lead wiper <b>102</b>. The inside surface of the body <b>120</b> of the follow wiper <b>104</b> includes a threaded portion <b>128</b>. In one embodiment, the threaded portion <b>128</b> may be disposed proximate the upper end of the follow wiper <b>104</b>, but in other embodiments, the threaded portion <b>128</b> may be disposed proximate the middle or lower end of the follow wiper <b>104</b>. As shown, the threaded portion <b>128</b> may be formed in the first diameter D<b>1</b><i>b </i>of the body <b>120</b>. In one embodiment, the threaded portion <b>128</b> may be a ratchet thread.

The lead and follow wipers <b>102</b>, <b>104</b> are initially run downhole on a lower end of a running tool <b>144</b> and positioned at the top of a liner (not shown) to be cemented. Thus, when the wiper plug system is initially run downhole, the lead wiper <b>102</b> is coupled to the follow wiper <b>104</b> and the follow wiper <b>104</b> is coupled to the lower end of the running tool <b>144</b>. Before cement is pumped downhole, the lead wiper <b>102</b> may be released or separated from the follow wiper <b>104</b> and run downhole until it lands in a landing collar (not shown). After the cement is pumped downhole, the follow wiper <b>104</b> may be released or separated from the running tool <b>144</b> and run downhole until it lands in the lead wiper <b>102</b> positioned in the landing collar (not shown). The lead wiper <b>102</b> may be coupled with the follow wiper <b>104</b> and the follow wiper <b>104</b> may be coupled with the running tool <b>144</b> as discussed below.

A first collet ring <b>130</b> is coupled to the lower end of the body <b>120</b> of the follow wiper <b>104</b>. The first collet ring <b>130</b> may be coupled to the body <b>120</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The first collet ring <b>130</b> includes at least one collet finger <b>132</b> extending axially downward and configured to engage the body <b>108</b> of the lead wiper <b>102</b>. One of ordinary skill in the art will appreciate that the first collet ring <b>130</b> may include a cylindrical ring having one or more collet fingers <b>132</b> extending therefrom or may include one or more collet fingers individually coupled to the follow wiper <b>104</b>.

As shown, the bore <b>116</b> of the lead wiper <b>102</b> may include a third diameter D<b>3</b><i>a </i>axially above the second diameter D<b>2</b><i>a </i>and larger than the first and second diameters D<b>1</b><i>a</i>, D<b>2</b><i>a</i>. A second shoulder <b>136</b> is formed between the second diameter D<b>2</b><i>a </i>and the third diameter D<b>3</b><i>a</i>. An upset <b>138</b> may be formed on the third diameter D<b>3</b><i>a </i>of the body <b>108</b>, thereby forming a groove <b>140</b> between the upset <b>138</b> and the second shoulder <b>136</b>. One of ordinary skill in the art will appreciate that the upset <b>138</b> may be a circumferential upset in the third diameter D<b>3</b><i>a </i>of the bore <b>116</b> of the body <b>108</b> or may be one or more individual upsets disposed circumferentially around the third diameter D<b>3</b><i>a </i>of the body <b>108</b>. The groove <b>140</b> is configured to receive a collet head <b>134</b> of the collet finger <b>132</b>, so as to couple the lead wiper <b>102</b> and the follow wiper <b>104</b>. The collet head <b>134</b> includes an extension portion that extends radially outward from the collet finger <b>132</b>, such that the extension portion engages the groove <b>140</b> of the lead wiper <b>102</b> body <b>108</b> and abuts the upset <b>138</b>.

A first sleeve <b>142</b> is disposed within the upper end of the body <b>108</b> of the lead wiper <b>102</b>. At least a portion of the first sleeve <b>142</b> may extend into the lower end of the follow wiper <b>104</b>. An inside diameter of the first sleeve <b>142</b> is approximately equal to the first diameter D<b>1</b><i>a </i>of the bore <b>116</b> of the lead wiper <b>102</b>. The first sleeve <b>142</b> has a first outer diameter S<b>1</b><i>a </i>and a second outer diameter S<b>2</b><i>a</i>, wherein the second outer diameter S<b>2</b><i>a </i>is smaller than the first outer diameter S<b>1</b><i>a</i>. When the follow wiper <b>104</b> and the lead wiper <b>102</b> are coupled together (e.g., when the lead and follow wipers <b>102</b>, <b>104</b> are run into the hole and positioned at the top of a liner) the first sleeve <b>142</b> may be disposed a selected axial distance above the shoulder <b>118</b> formed between the first and second diameters D<b>1</b><i>a</i>, D<b>2</b><i>a </i>of the bore <b>116</b> of the lead wiper <b>102</b>. In this engaged or run-in position, the first outer diameter S<b>1</b><i>a </i>of the first sleeve <b>142</b> contacts the inner surface of the collet head <b>134</b> of the at least one collet finger <b>132</b>, thereby maintaining the collet head <b>134</b> in the groove <b>140</b> of the lead wiper <b>102</b> body <b>108</b>. Contact between the collet head <b>134</b> and the upset <b>138</b> of the lead wiper <b>102</b> body <b>108</b> maintains engagement of the lead and follow wipers <b>102</b>, <b>104</b>.

A second collet ring <b>151</b> is coupled to the lower end of the running tool <b>144</b>. The second collet ring <b>151</b> may be coupled to the running tool <b>144</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The second collet ring <b>151</b> includes at least one collet finger <b>154</b> extending axially downward and configured to engage the body <b>120</b> of the follow wiper <b>104</b>. One of ordinary skill in the art will appreciate that the second collet ring <b>151</b> may include a cylindrical ring having one or more collet fingers <b>154</b> extending therefrom or may include one or more collet fingers individually coupled to the running tool <b>144</b>.

As shown, the bore <b>124</b> of the follow wiper <b>104</b> may include a third diameter D<b>3</b><i>b </i>axially above the second diameter D<b>2</b><i>b </i>and larger than the first and second diameters D<b>1</b><i>b</i>, D<b>2</b><i>b</i>. A second shoulder <b>146</b> is formed between the second diameter D<b>2</b><i>b </i>and the third diameter D<b>3</b><i>b</i>. An upset <b>148</b> may be formed on the third diameter D<b>3</b><i>b </i>of the body <b>120</b>, thereby forming a groove <b>150</b> between the upset <b>148</b> and the second shoulder <b>146</b>. One of ordinary skill in the art will appreciate that the upset <b>148</b> may be a circumferential upset in the third diameter D<b>3</b><i>b </i>of the bore <b>124</b> of the body <b>120</b> or may be one or more individual upsets disposed circumferentially around the third diameter D<b>3</b><i>b </i>of the body <b>120</b>. The groove <b>150</b> is configured to receive a collet head <b>152</b> of the collet finger <b>154</b>, so as to couple the follow wiper <b>104</b> and the running tool <b>144</b>. The collet head <b>152</b> includes an extension portion that extends radially outward from the collet finger <b>154</b>, such that the extension portion engages the groove <b>150</b> of the follow wiper <b>104</b> body <b>120</b> and abuts the upset <b>148</b>.

A second sleeve <b>156</b> is disposed within the upper end of the body <b>120</b> of the follow wiper <b>104</b>. At least a portion of the second sleeve <b>156</b> may extend into the lower end of the running tool <b>144</b>. An inside diameter of the second sleeve <b>156</b> is approximately equal to or less than the first diameter D<b>1</b><i>b </i>of the bore <b>124</b> of the follow wiper <b>104</b>. The second sleeve <b>156</b> has a first outer diameter S<b>1</b><i>b </i>and a second outer diameter S<b>2</b><i>b</i>, wherein the second outer diameter S<b>2</b><i>b </i>is smaller than the first outer diameter S<b>1</b><i>b</i>. When the follow wiper <b>104</b> and the running tool <b>144</b> are coupled together (e.g., when the lead and follow wipers <b>102</b>, <b>104</b> are run into the hole and positioned at the top of a liner) the second sleeve <b>156</b> may be disposed a selected axial distance above the shoulder <b>126</b> formed between the first and second diameters D<b>1</b><i>b</i>, D<b>2</b><i>b </i>of the bore <b>124</b> of the follow wiper <b>104</b>. In this engaged or run-in position, the first outer diameter S<b>1</b><i>b </i>of the second sleeve <b>156</b> contacts the inner surface of the collet head <b>152</b> of the at least one collet finger <b>154</b>, thereby maintaining the collet head in the groove <b>150</b> of the follow wiper <b>104</b> body <b>120</b>. Contact between the collet head <b>152</b> and the upset <b>148</b> of the follow wiper <b>104</b> body <b>120</b> maintains engagement of the follow wiper <b>104</b> and the running tool <b>144</b>.

Once the coupled lead and follow wipers <b>102</b>, <b>104</b> are run downhole on the running tool <b>144</b> and positioned at the top of the liner to be cemented, the lead wiper <b>102</b> may be decoupled from the follow wiper <b>104</b> and run downhole. The lead wiper <b>102</b> is moved downhole by of a volume of cement pumped down into the bore of the liner behind the lead wiper <b>102</b> until the lead wiper <b>102</b> seats within a landing collar (not shown) positioned proximate a distal end of the liner (not shown).

To decouple the lead wiper <b>102</b> from the follow wiper <b>104</b>, a first drill pipe pump down plug (“PDP”) may be released from the surface into the drill string. As shown in <figref idref="DRAWINGS">FIG. 1B</figref>, the first PDP <b>158</b> includes a solid body <b>160</b> and a tail portion <b>162</b>. The body <b>160</b> and the tail portion <b>162</b> of the PDP <b>158</b> may be separate components coupled together by any means known in the art, for example, by threaded engagement, press-fit, welding, etc., or may be integrally formed. One or more fins <b>164</b> are disposed on the tail portion <b>162</b> and may be formed from any material known in the art, for example, an elastomer. The fins <b>164</b> are configured to flex or compress when the PDP <b>158</b> is run into a tubular or component having an inner diameter smaller than a maximum diameter of the fins <b>164</b> in an expanded state. The body <b>160</b> includes a rounded nose portion <b>166</b> having an outer diameter approximately equal to or less than the first diameter D<b>1</b><i>a </i>of bore <b>116</b> of the lead wiper <b>102</b>. A split ring <b>168</b> may be disposed around the body <b>160</b> of the first PDP <b>158</b> proximate the nose portion <b>166</b>. An outer surface of the split ring <b>168</b> may include a threaded portion. In one embodiment, the outer surface of the split ring <b>168</b> may include a ratchet thread configured to engage the threaded portion <b>114</b> disposed on the inside surface of the body <b>108</b> of the lead wiper <b>102</b>. Additionally, an inside diameter of the first sleeve <b>142</b> may also include a corresponding thread, such that when the first PDP <b>158</b> is dropped in the bore <b>116</b> of the lead wiper <b>102</b>, the first PDP <b>158</b> may be secured to both the body <b>108</b> and the sleeve <b>142</b>. This threaded engagement may enhance the seal of the first PDP <b>158</b> within the lead wiper <b>102</b>.

As shown, an inside diameter of the first sleeve <b>142</b> proximate the upper end of the first sleeve <b>142</b> is larger than the inside diameter of the first sleeve <b>142</b> proximate the lower end of the first sleeve <b>142</b>. The inside diameter of the first sleeve <b>142</b> may gradually change from a first diameter to a smaller diameter (i.e., the inside surface of the first sleeve <b>142</b> may be sloped) or the first sleeve <b>142</b> may include a first diameter and a second diameter forming a shoulder therebetween. In one embodiment, the maximum outside diameter of the first PDP <b>158</b> is approximately equal to or greater than a minimum inside diameter of the first sleeve <b>142</b>. As such, when the first PDP <b>158</b> is run downhole, the first PDP <b>158</b> becomes wedged within or engages the first sleeve <b>142</b>. In this embodiment, the split ring <b>168</b> of the first PDP <b>158</b> is located such that at least a portion of the split ring <b>168</b> extends downwardly below a lower surface of the first sleeve <b>142</b>.

Referring to both <figref idref="DRAWINGS">FIGS. 1A and 1B</figref>, hydraulic pressure applied behind the first PDP <b>158</b> by the pumped volume of cement (not shown) causes the first PDP <b>158</b> to move the first sleeve <b>142</b> axially downward until the first sleeve <b>142</b> engages the shoulder <b>118</b> of the body <b>108</b> of the lead wiper <b>102</b>. As the first sleeve <b>142</b> moves axially downward, the first outer diameter S<b>1</b><i>a </i>of the first sleeve <b>146</b> moves downward until it is no longer in contact engagement with the collet head <b>134</b> of the first collet ring <b>130</b>. Accordingly, the second outer diameter S<b>2</b><i>a </i>is moved downward and spaced radially next to the collet head <b>134</b>. Because the second outer diameter S<b>2</b><i>a </i>is smaller than the first outer diameter S<b>1</b><i>a</i>, a gap is provided between the collet head <b>134</b> and the first sleeve <b>146</b>. The split ring <b>168</b> of the first PDP <b>158</b> engages the threaded portion <b>114</b> of the body <b>108</b> of the lead wiper <b>102</b>. In an embodiment where the threaded portion <b>114</b> is a ratchet thread and the split ring <b>168</b> includes a ratchet thread on the outer surface, the engaged ratchet threads securely couple the first PDP <b>158</b> to the lead wiper <b>102</b> and prevent the first PDP <b>158</b> from moving axially upward. The first PDP <b>158</b> seals the bore <b>116</b> of the lead wiper <b>102</b> through engagement with the first sleeve <b>146</b>. Thus, as the hydraulic pressure of the volume of cement is continuously applied behind the first PDP <b>158</b>, the at least one collet finger <b>132</b> may flex radially inward allowing the collet head <b>142</b> to engage the second outer diameter S<b>2</b><i>a </i>of the first sleeve <b>146</b> and disengage from the groove <b>140</b> of the lead wiper <b>102</b> body <b>108</b>, thereby decoupling the lead wiper <b>102</b> from the follow wiper <b>104</b>.

<figref idref="DRAWINGS">FIG. 1C</figref> shows the lead wiper <b>102</b> disengaged from the follow wiper <b>104</b> (<figref idref="DRAWINGS">FIG. 1A</figref>) having the first PDP <b>158</b> coupled therein by the split ring <b>168</b> engaged with the inside surface of the body <b>108</b> and the outer diameter of the first PDP <b>158</b> engaged with the inside diameter of the first sleeve <b>146</b>. The lead wiper <b>102</b> is then pumped downhole in front of the volume of cement, while the follow wiper <b>104</b> (<figref idref="DRAWINGS">FIG. 1A</figref>) remains coupled to the running tool <b>144</b> (<figref idref="DRAWINGS">FIG. 1A</figref>) at the top of the liner (not shown).

<figref idref="DRAWINGS">FIG. 1D</figref> shows the follow wiper <b>104</b> coupled to the running tool <b>144</b> after the lead wiper <b>102</b> (<figref idref="DRAWINGS">FIG. 1C</figref>) has been decoupled from the follow wiper <b>104</b> and run downhole. Once a predetermined volume of cement has been pumped downhole for cementing a liner in place in a borehole, the follow wiper <b>104</b> may be decoupled from the running tool <b>144</b> and run downhole to remove any excess cement from the inside wall of the liner (not shown). To decouple the follow wiper <b>104</b> from the running tool <b>144</b>, a second PDP <b>170</b> may be released from the surface after the volume of cement has been pumped downhole. Drilling fluid may be pumped behind the second PDP <b>170</b> to push the second PDP <b>170</b> down hole into the bore <b>124</b> of the follow wiper <b>104</b>. A maximum outside diameter of the second PDP <b>170</b> is greater than the maximum outside diameter of the first PDP <b>168</b> (<figref idref="DRAWINGS">FIG. 1C</figref>). Further, the maximum outside diameter of the first PDP <b>168</b> is smaller than a minimum inside diameter of the second sleeve <b>156</b> disposed in follow wiper <b>104</b> or any inside diameter of the body <b>120</b> of the follow wiper <b>104</b>. As will be described in more detail below, the maximum outside diameter of the second PDP <b>170</b> is greater than at least the minimum inside diameter of the second sleeve <b>156</b> disposed in the follow wiper <b>104</b>.

As shown in <figref idref="DRAWINGS">FIG. 1D</figref>, the second PDP <b>170</b> includes a solid body <b>172</b> and a tail portion <b>176</b>. The body <b>172</b> and the tail portion <b>176</b> of the second PDP <b>170</b> may be separate components coupled together by any means known in the art, for example, by threaded engagement, press-fit, welding, etc., or may be integrally formed. One or more fins <b>178</b> are disposed on the tail portion <b>176</b> and may be formed from any material known in the art, for example, an elastomer. The fins <b>178</b> are configured to flex or compress when the PDP <b>170</b> is run into a tubular or component having an inner diameter smaller than a maximum diameter of the fins <b>178</b> in an expanded state. The body <b>172</b> includes a rounded nose portion <b>174</b> having an outer diameter approximately equal to or less than the first diameter D<b>1</b><i>b </i>of bore <b>124</b> of the follow wiper <b>104</b>. A split ring <b>180</b> may be disposed around the body <b>172</b> of the second PDP <b>170</b> proximate the nose portion <b>174</b>. An outer surface of the split ring <b>180</b> may include a threaded portion. In one embodiment, the outer surface of the split ring <b>180</b> may include a ratchet thread configured to engage the threaded portion <b>128</b> disposed on the inside surface of the body <b>120</b> of the follow wiper <b>104</b>.

As shown, an inside diameter of the second sleeve <b>156</b> proximate the upper end of the second sleeve <b>156</b> is larger than the inside diameter of the second sleeve <b>156</b> proximate the lower end of the second sleeve <b>156</b>. The inside diameter of the second sleeve <b>156</b> may gradually change from a first diameter to a smaller diameter (i.e., the inside surface of the second sleeve <b>156</b> may be sloped) or the second sleeve <b>156</b> may include a first diameter and a second diameter forming a shoulder therebetween. In one embodiment, the maximum outside diameter of the second PDP <b>170</b> is approximately equal to or greater than a minimum inside diameter of the second sleeve <b>156</b>. As such, when the second PDP <b>170</b> is run downhole, the second PDP <b>170</b> becomes wedged within or engages the second sleeve <b>156</b>. In this embodiment, the split ring <b>180</b> of the second PDP <b>170</b> is located such that at least a portion of the split ring <b>180</b> extends downwardly below a lower surface of the second sleeve <b>180</b>.

Referring to both <figref idref="DRAWINGS">FIGS. 1A and 1D</figref>, hydraulic pressure applied behind the second PDP <b>170</b> by the pumped drill fluid (not shown) causes the second PDP <b>170</b> to move the second sleeve <b>156</b> axially downward until the second sleeve <b>156</b> engages the shoulder <b>126</b> of the body <b>120</b> of the follow wiper <b>104</b>. As the second sleeve <b>156</b> moves axially downward, the first outer diameter S<b>1</b><i>b </i>of the second sleeve <b>156</b> moves downward until it is no longer in contact engagement with the collet head <b>152</b> of the second collet ring <b>151</b>. Accordingly, the second outer diameter S<b>2</b><i>b </i>is moved downward and spaced radially next to the collet head <b>152</b>. Because the second outer diameter S<b>2</b><i>b </i>is smaller than the first outer diameter S<b>1</b><i>b</i>, a gap is provided between the collet head <b>152</b> and the second sleeve <b>156</b>. The split ring <b>180</b> of the second PDP <b>170</b> engages the threaded portion <b>128</b> of the body <b>120</b> of the follow wiper <b>104</b>. In an embodiment where the threaded portion <b>128</b> is a ratchet thread and the split ring <b>180</b> includes a ratchet thread on the outer surface, the engaged ratchet threads securely couple the second PDP <b>170</b> to the follow wiper <b>104</b> and prevent the second PDP <b>170</b> from moving axially upward. Additionally, an inside diameter of the second <b>156</b> may also include a corresponding thread, such that when the second PDP <b>170</b> is dropped in the bore <b>124</b> of the follow wiper <b>104</b>, the second PDP <b>170</b> may be secured to both the body <b>120</b> and the sleeve <b>156</b>. This threaded engagement may enhance the seal of the second PDP <b>170</b> within the follow wiper <b>104</b>. The second PDP <b>170</b> seals the bore <b>124</b> of the follow wiper <b>104</b> through engagement with the second sleeve <b>156</b>. Thus, as the hydraulic pressure of the drill fluid is continuously applied behind the second PDP <b>170</b>, the at least one collet finger <b>154</b> may flex radially inward allowing the collet head <b>152</b> to engage the second outer diameter S<b>2</b><i>b </i>of the second sleeve <b>156</b> and disengage from the groove <b>150</b> of the follow wiper <b>104</b> body <b>120</b>, thereby decoupling the follow wiper <b>104</b> from the running tool <b>144</b>.

<figref idref="DRAWINGS">FIG. 1E</figref> shows the follow wiper <b>104</b> disengaged from the running tool <b>144</b> (<figref idref="DRAWINGS">FIG. 1A</figref>) having the second PDP <b>170</b> coupled therein by the split ring <b>180</b> engaged with the inside surface of the body <b>120</b> and the outer diameter of the second PDP <b>170</b> engaged with the inside diameter of the second sleeve <b>156</b>. The follow wiper <b>104</b> is then pumped downhole behind the volume of cement by the hydraulic force of drill fluid applied behind the follow wiper <b>104</b>. As the follow wiper <b>104</b> moves downhole, the at least one wiping fin <b>106</b><i>b </i>contacts the inner wall of the liner and scrapes or removes any excess cement from the liner wall downward in front of the follow wiper <b>104</b>.

<figref idref="DRAWINGS">FIGS. 2A-2F</figref> show another dual wiper plug system <b>200</b> in accordance with embodiments of the present disclosure. Dual wiper plug system <b>200</b> includes a lead wiper <b>202</b> and a follow wiper <b>204</b>. Each of the lead wiper <b>202</b> and the follow wiper <b>204</b> include one or more wiping fins <b>206</b> disposed circumferentially around the body of the wiper <b>202</b>, <b>204</b> and extending radially therefrom to contact and seal against an inner wall of a liner (not shown). The wiping fins <b>206</b> may be formed from an elastomeric material or any other know material in the art such that the wiping fins <b>206</b> are configured to flex or compress as the wiper is run through a liner or other tubular component having an inside diameter smaller than a maximum diameter of the wiping fins <b>206</b> in an expanded state.

<figref idref="DRAWINGS">FIG. 2A</figref> shows the lead wiper <b>202</b> coupled to the follow wiper <b>204</b> and the follow wiper coupled to a running tool <b>244</b> in a run-in position. The lead wiper <b>202</b> includes a tubular body <b>208</b> and a nose <b>210</b> disposed on a lower end of the body <b>208</b>. The one or more wiping fins <b>206</b><i>a </i>are coupled to the body <b>208</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. The nose <b>210</b> includes one or more ports <b>212</b> to allow fluid flow from inside the body <b>208</b> to outside the body <b>208</b>. A snap ring <b>219</b> may be disposed around the lead wiper <b>202</b> proximate the nose <b>210</b> and axially above the ports <b>212</b>. The snap ring <b>219</b> may include a threaded outer surface configured to engage a corresponding threaded surface of the landing collar (not shown) to secure the lead wiper <b>202</b> in the landing collar (not shown). In one embodiment, the threaded outer surface of the snap ring <b>219</b> and the corresponding threaded surface of the landing collar (not shown) may be ratchet threads, so as to prevent the lead wiper <b>202</b> from moving axially upward when engaged. A bolt <b>227</b> or a key may be disposed in the snap ring <b>219</b> and configured to engage the snap ring <b>219</b> to the lead wiper <b>202</b> to prevent rotation of the lead wiper <b>202</b> and components of the lead wiper <b>202</b> when the lead wiper <b>202</b> is milled up after completion of the cementing process.

The body <b>208</b> includes a bore <b>216</b> therethrough. The lead wiper <b>202</b> includes at least one sleeve <b>211</b> disposed in the bore <b>216</b>. The at least one sleeve <b>211</b> includes a threaded portion <b>214</b> disposed on the inner surface of the sleeve <b>211</b>. In one embodiment, the threaded portion <b>214</b> may be a ratchet thread. In certain embodiments, the lead wiper <b>202</b> may include a first sleeve <b>211</b> and a second sleeve <b>213</b> coupled to the first sleeve <b>211</b>, wherein a threaded portion <b>214</b> may be disposed on the inner surface of one of the first sleeve <b>211</b> and the second sleeve <b>213</b>. As shown, the second sleeve <b>213</b> may be disposed axially below the first sleeve <b>211</b>. In the run-in position, the first and second sleeves <b>211</b>, <b>213</b> are positioned axially above the ports <b>212</b>, such that the ports <b>212</b> are open. In one embodiment, the threaded portion <b>214</b> may be disposed proximate the upper end of the lead wiper <b>202</b>, but in other embodiments, the threaded portion <b>214</b> may be disposed proximate the middle or lower end of the lead wiper <b>202</b>.

One or more axial slots <b>231</b> may be formed in the body <b>208</b> of the lead wiper <b>202</b> configured to engage one or more anti-rotation devices <b>233</b> coupled to the first sleeve <b>211</b>. The anti-rotation devices <b>233</b> may include a bolt or a key configured to fit within the axial slots <b>231</b> and prevent rotation of the first sleeve <b>211</b> when the lead wiper <b>202</b> and components of the lead wiper <b>202</b> are milled up after completion of the cementing process. The anti-rotation devices <b>233</b> are configured to move axially within the one or more axial slots <b>231</b> when the first sleeve <b>211</b> shifts axially downward, but are prevented from rotating. Preventing rotation of the components of the lead wiper <b>202</b> during milling up may provide a quicker, more efficient milling process. Similarly, one or more slots <b>235</b> may be formed in the body <b>220</b> of the follow wiper <b>204</b> configured to engage one or more anti-rotation devices <b>237</b> coupled to the sleeve <b>215</b> of the follow wiper <b>204</b>. The anti-rotation devices <b>237</b> may include a bolt or a key configured to fit within the slots <b>235</b> and prevent rotation of the sleeve <b>215</b> when the follow wiper <b>204</b> and the components of the follow wiper <b>204</b> are milled up.

The follow wiper <b>204</b> includes a tubular body <b>220</b> and a landing nose <b>222</b> disposed on a lower end of the tubular body <b>220</b>. In one embodiment, a lower end of the landing nose <b>222</b> may include a plurality of castellations <b>283</b>, as shown in <figref idref="DRAWINGS">FIG. 4</figref>. The castellations <b>283</b> are configured to provide quicker and more efficient milling up of the follow wiper <b>204</b> after landing in the landing collar (not shown). As shown in <figref idref="DRAWINGS">FIG. 2A</figref>, the one or more wiping fins <b>206</b><i>b </i>are coupled to the body <b>220</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. A snap ring <b>221</b> may be disposed around the follow wiper <b>204</b> proximate the landing nose <b>222</b>. The snap ring <b>221</b> may include a threaded outer surface configured to engage a corresponding threaded surface of the landing collar (not shown) to secure the follow wiper <b>204</b> in the landing collar (not shown). In one embodiment, the threaded outer surface of the snap ring <b>221</b> and the corresponding threaded surface of the landing collar (not shown) may be ratchet threads, so as to prevent the follow wiper <b>204</b> from moving axially upward when engaged. A bolt <b>229</b> or a key may be disposed in the snap ring <b>221</b> and configured to engage the snap ring <b>221</b> to the follow wiper <b>204</b> to prevent rotation of the follow wiper <b>204</b> and components of the follow wiper <b>204</b> when the follow wiper <b>204</b> is milled up after completion of the cementing process.

The body <b>220</b> of the follow wiper <b>204</b> includes a bore <b>224</b> therethrough. The follow wiper <b>204</b> includes a sleeve <b>215</b> disposed in the bore <b>224</b>. The sleeve <b>215</b> includes an internal shoulder <b>217</b>, such that an inside diameter of the sleeve <b>215</b> proximate the upper end of the shoulder <b>217</b> is larger than an inside diameter of the sleeve <b>215</b> proximate the lower end of the shoulder <b>217</b>. The shoulder may be sloped or may be formed as a right angle. As shown, the lower end of the sleeve <b>215</b> may be configured to receive the upper end of the first sleeve <b>211</b> of the lead wiper <b>202</b> within the bore <b>224</b>.

A first collet ring <b>230</b> is coupled to the upper end of the body <b>208</b> of the lead wiper <b>202</b>. The first collet ring <b>230</b> may be coupled to the body <b>220</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The first collet ring <b>230</b> includes at least one collet finger <b>232</b> extending axially upward and configured to engage the body <b>220</b> of the follow wiper <b>204</b>. One of ordinary skill in the art will appreciate that the first collet ring <b>230</b> may include a cylindrical ring having one or more collet fingers <b>232</b> extending therefrom or may include one or more collet fingers individually coupled to the lead wiper <b>202</b>. At least one shear screw <b>223</b> may be engaged with the first collet ring <b>230</b> and extend radially inward to engage a groove <b>225</b> formed in an outer surface of the first sleeve <b>211</b>.

The one or more collet fingers <b>232</b> each include a collet head <b>234</b> configured to engage a groove <b>240</b> formed on the inner surface of the body <b>220</b>, so as to couple the lead wiper <b>202</b> and the follow wiper <b>204</b>. The collet head <b>234</b> includes an extension portion that extends radially outward from the collet finger <b>232</b>, such that the extension portion engages the groove <b>234</b> of the follow wiper <b>204</b> body <b>220</b> and abuts an upset <b>238</b> formed on the inner surface of the body <b>220</b> axially below the groove <b>240</b>.

When the follow wiper <b>204</b> and the lead wiper <b>202</b> are coupled together (e.g., when the lead and follow wipers <b>202</b>, <b>204</b> are run into the hole and positioned at the top of a liner) an outer diameter of the first sleeve <b>211</b> contacts the inner surface of the collet head <b>234</b> of the at least one collet finger <b>232</b>, thereby maintaining the collet head <b>234</b> in the groove <b>240</b> of the follow wiper <b>204</b> body <b>220</b>. Contact between the collet head <b>234</b> and the upset <b>238</b> of the follow wiper <b>204</b> body <b>220</b> maintains engagement of the lead and follow wipers <b>202</b>, <b>204</b>.

A second collet ring <b>251</b> is coupled to the lower end of the running tool <b>244</b>. The second collet ring <b>251</b> may be coupled to the running tool <b>244</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The second collet ring <b>251</b> includes at least one collet finger <b>254</b> extending axially downward and configured to engage the body <b>220</b> of the follow wiper <b>204</b>. One of ordinary skill in the art will appreciate that the second collet ring <b>251</b> may include a cylindrical ring having one or more collet fingers <b>254</b> extending therefrom or may include one or more collet fingers <b>254</b> individually coupled to the running tool <b>244</b>. At least one shear screw <b>243</b> may be engaged with the second collet ring <b>251</b> and extend radially inward to engage a groove <b>245</b> formed in an outer surface of the sleeve <b>215</b>.

The one or more collet fingers <b>254</b> each include a collet head <b>252</b> configured to engage a groove <b>250</b> formed on the inner surface of the body <b>220</b>, so as to couple the follow wiper <b>204</b> to the running tool <b>244</b>. The collet head <b>252</b> includes an extension portion that extends radially outward from the collet finger <b>254</b>, such that the extension portion engages the groove <b>250</b> of the follow wiper <b>204</b> body <b>220</b> and abuts an upset <b>248</b>. The upset <b>248</b> may be formed on the inner surface of the body <b>220</b> axially above the groove <b>250</b> or the upset <b>248</b> may be formed by a secondary ring <b>253</b> coupled to the body <b>220</b> of the follow wiper <b>204</b>.

When the follow wiper <b>204</b> and the running tool <b>244</b> are coupled together (e.g., when the lead and follow wipers <b>202</b>, <b>204</b> are run into the hole and positioned at the top of a liner) an outer diameter of the sleeve <b>215</b> of the follow wiper <b>204</b> contacts the inner surface of the collet head <b>252</b> of the at least one collet finger <b>254</b>, thereby maintaining the collet head <b>252</b> in the groove <b>250</b> of the follow wiper <b>202</b> body <b>220</b>. Contact between the collet head <b>252</b> and the upset <b>248</b> of the follow wiper <b>202</b> body <b>220</b> maintains engagement of the follow wiper <b>204</b> and the running tool <b>244</b>.

To decouple the lead wiper <b>202</b> from the follow wiper <b>204</b>, a first PDP <b>258</b> may be released from the surface into the drill string. As shown in <figref idref="DRAWINGS">FIG. 2B</figref>, the first PDP <b>258</b> may be configured similar to the first PDP <b>158</b> described above with reference to <figref idref="DRAWINGS">FIG. 1B</figref>. When the first PDP <b>258</b> is run downhole, the first PDP <b>258</b> becomes engaged with the first sleeve <b>211</b> of the lead wiper <b>202</b>. In this embodiment, a split ring <b>268</b> of the first PDP <b>258</b> engages the threaded portion <b>214</b> disposed on the inner surface of the sleeve <b>211</b> to secure the first PDP <b>258</b> within the lead wiper <b>202</b> and seal the bore <b>216</b> of the lead wiper <b>202</b>. An outer surface of the split ring <b>268</b> may include a ratchet thread and the threaded portion <b>214</b> of the sleeve <b>211</b> may be a corresponding ratchet thread, such that engagement of the threaded portions provides locking engagement of the first PDP <b>258</b> with the lead wiper <b>202</b> that prevents the first PDP <b>258</b> from moving axially upward.

Referring to both <figref idref="DRAWINGS">FIGS. 2A and 2B</figref>, hydraulic pressure applied behind the first PDP <b>258</b> by the pumped volume of cement (not shown) causes the first PDP <b>258</b> to move the first sleeve <b>211</b> axially downward, shearing the shear pins <b>223</b>, until the second sleeve <b>213</b> engages or abuts an inside surface of the nose <b>210</b> of the lead wiper <b>102</b>. When the second sleeve <b>213</b> engages the nose <b>210</b>, the ports <b>212</b> are closed by the sleeve <b>213</b>. The first sleeve <b>211</b> may include a snap ring <b>287</b> disposed in a circumferential groove <b>289</b> formed in an outer surface of the first sleeve <b>211</b>. The snap ring <b>287</b> and circumferential groove <b>289</b> may be located axially below the groove <b>225</b> formed in the first sleeve <b>211</b> configured to receive at least one shear screw <b>223</b>. The snap ring <b>287</b> may be biased radially outward. In the run-in position, the snap ring <b>287</b> is compressed within the groove <b>289</b> by contact engagement with the inner surface of the first collet ring <b>230</b>. As the first sleeve <b>211</b> moves axially downward, the snap ring <b>287</b> may radially align with a groove or shoulder <b>201</b> on the inside diameter of the body <b>208</b> of the lead wiper <b>202</b>, thereby allowing the snap ring <b>287</b> to expand radially outward to secure the first sleeve <b>211</b> to the body <b>208</b>.

The first sleeve <b>211</b> also includes a groove <b>241</b> or a reduced outer diameter portion. When the tool is run-in, the groove <b>241</b> is spaced axially above the collet head <b>234</b> a distance approximately equal to the distance between a lower surface of the second sleeve <b>213</b> and the inside surface of the nose <b>210</b>. Thus, when the first sleeve <b>211</b> moves axially downward, the groove <b>241</b> moves into radial alignment with the collet head <b>234</b> of the first collet ring <b>230</b>. As the hydraulic pressure of the volume of cement is continuously applied behind the first PDP <b>258</b>, the at least one collet finger <b>232</b> may flex radially inward allowing the collet head <b>234</b> to engage the groove <b>241</b> of the first sleeve <b>211</b> and disengage from the groove <b>240</b> and the upset <b>238</b> of the lead wiper <b>202</b> body <b>208</b>, thereby decoupling the lead wiper <b>202</b> from the follow wiper <b>204</b>.

<figref idref="DRAWINGS">FIG. 2C</figref> shows the lead wiper <b>202</b> disengaged from the follow wiper <b>204</b> (<figref idref="DRAWINGS">FIG. 2A</figref>) having the first PDP <b>258</b> coupled therein by the split ring <b>268</b> engaged with the inside surface of the sleeve <b>211</b>. The lead wiper <b>202</b> is then pumped downhole in front of the volume of cement, while the follow wiper <b>204</b> (<figref idref="DRAWINGS">FIG. 2A</figref>) remains coupled to the running tool <b>244</b> (<figref idref="DRAWINGS">FIG. 2A</figref>) at the top of the liner (not shown).

<figref idref="DRAWINGS">FIGS. 2D and 2E</figref> show the follow wiper <b>204</b> coupled to the running tool <b>244</b> after the lead wiper <b>202</b> (<figref idref="DRAWINGS">FIG. 2C</figref>) has been decoupled from the follow wiper <b>204</b> and run downhole. Once a predetermined volume of cement has been pumped downhole for cementing a liner in place in a borehole, the follow wiper <b>204</b> may be decoupled from the running tool <b>244</b> and run downhole to remove any excess cement from the inside wall of the liner (not shown). To decouple the follow wiper <b>204</b> from the running tool <b>244</b>, a second PDP <b>270</b> may be released from the surface after the volume of cement has been pumped downhole. Drilling fluid may be pumped behind the second PDP <b>270</b> to push the second PDP <b>270</b> down hole into the bore <b>224</b> of the follow wiper <b>204</b>. A split ring <b>280</b> is disposed around the body <b>272</b> of the second PDP <b>270</b> proximate the nose portion <b>274</b>. The split ring <b>280</b> may include a latching mechanism <b>271</b>, for example a c-ring with a lip, a collet finger, or latching dog, configured to engage the shoulder <b>217</b> of the sleeve <b>215</b> of the follow wiper <b>204</b>. The latching mechanism <b>271</b> may include an axial portion and an extension portion such that the axial portion is configured to flex radially inward as the extension portion passes through the shoulder <b>217</b> and radially outward after the extension portion has passed through the shoulder <b>217</b>. The extension portion may then be engaged with the shoulder <b>217</b> such that the second PDP <b>270</b> may not move axially upward. In other embodiments, an outer surface of the split ring <b>280</b> may include a threaded portion. In one embodiment, the outer surface of the split ring <b>280</b> may include a ratchet thread configured to engage a threaded portion (not shown) disposed on the inside surface of the body <b>220</b> of the follow wiper <b>204</b>.

As shown in <figref idref="DRAWINGS">FIG. 2E</figref>, the second PDP <b>270</b> is similar to the second PDP <b>170</b> described above with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The outside diameter of the body <b>272</b> of the PDP <b>270</b> is approximately equal to or slightly less than the inside diameter of the sleeve <b>215</b>. When the second PDP <b>270</b> is run downhole, the second PDP <b>270</b> engages the shoulder <b>217</b> of the sleeve <b>215</b>, thereby sealing the bore <b>224</b> of the follow wiper <b>204</b>.

Referring to both <figref idref="DRAWINGS">FIGS. 2A and 2E</figref>, hydraulic pressure applied behind the engaged second PDP <b>270</b> by the pumped drill fluid (not shown) causes the second PDP <b>270</b> to move the sleeve <b>215</b> axially downward until the sleeve <b>215</b> engages a shoulder <b>249</b> formed on the inside of the body <b>220</b> of the follow wiper <b>204</b>. As the sleeve <b>215</b> moves, the shear screws <b>243</b> are sheared. The first sleeve <b>215</b> includes a groove <b>281</b> or a reduced outer diameter portion. When the tool is run-in, the groove <b>281</b> is spaced axially above the collet head <b>252</b> a distance approximately equal to the distance between a lower surface of the sleeve <b>215</b> and the shoulder <b>249</b>. Thus, when the sleeve <b>215</b> moves axially downward, the groove <b>281</b> moves into radial alignment with the collet head <b>252</b> of the second collet ring <b>251</b>. As the hydraulic pressure of the volume of drill fluid is continuously applied behind the second PDP <b>270</b>, the at least one collet finger <b>254</b> may flex radially inward allowing the collet head <b>252</b> to engage the groove <b>281</b> of the sleeve <b>215</b> and disengage from the groove <b>250</b> and the upset <b>248</b> of the follow wiper <b>204</b> body <b>220</b>, thereby decoupling the follow wiper <b>204</b> from the running tool <b>244</b>.

<figref idref="DRAWINGS">FIG. 2F</figref> shows the follow wiper <b>204</b> disengaged from the running tool <b>244</b> (<figref idref="DRAWINGS">FIG. 2E</figref>) having the second PDP <b>270</b> coupled therein by the split ring <b>280</b> engaged with the inside surface of the sleeve <b>215</b>. The follow wiper <b>204</b> is then pumped downhole behind the volume of cement by the hydraulic force of drilling fluid applied behind the follow wiper <b>204</b>. As the follow wiper <b>204</b> moves downhole, the at least one wiping fin <b>206</b><i>b </i>contacts the inner wall of the liner and scrapes or removes any excess cement from the liner wall downward in front of the follow wiper <b>204</b>.

In the event that the second PDP <b>270</b> (<figref idref="DRAWINGS">FIG. 2E</figref>) is mistakenly dropped into the well before the first PDP <b>258</b> (<figref idref="DRAWINGS">FIG. 2A</figref>), the dual plug system <b>200</b> disclosed herein is configured to prevent premature decoupling of the follow wiper <b>204</b> from the running tool <b>244</b> if the lead wiper <b>202</b> is still coupled to the follow wiper <b>204</b>. That is, the follow wiper <b>204</b> is prevented from decoupling from the dual plug system <b>200</b> if the lead wiper <b>202</b> has not yet been decoupled from the dual plug system <b>200</b>.

As shown in <figref idref="DRAWINGS">FIG. 3</figref>, where like reference characters represent like parts, in the event that the second PDP <b>270</b> is mistakenly dropped before the first PDP <b>258</b> (<figref idref="DRAWINGS">FIG. 2A</figref>), the first PDP <b>270</b> runs into the sleeve <b>215</b> of the follow wiper <b>204</b> until the outer diameter of the PDP <b>270</b> contacts the internal shoulder <b>217</b> of the follow wiper <b>204</b>. Because the lead wiper <b>202</b> is still coupled to the follow wiper <b>204</b>, the upper surface of the first sleeve <b>211</b> of the lead wiper <b>202</b> abuts a lower surface of the shoulder <b>217</b> of the follow wiper <b>204</b> sleeve <b>215</b>. As such, the latching mechanism <b>271</b> of the split ring <b>280</b> of the second PDP <b>270</b> does not fully engage the internal shoulder <b>217</b> of the sleeve <b>215</b>. The internal shoulder <b>217</b> provides a load bearing surface on the sleeve <b>215</b> of the follow wiper <b>204</b> as pressure is applied from above the second PDP <b>270</b>, thereby preventing pressure from being applied to the first sleeve <b>211</b> of the lead wiper <b>202</b>. Because pressure is not applied to the first sleeve <b>211</b> of the lead wiper <b>202</b>, the shear screws <b>223</b> securing the first sleeve <b>211</b> to the first collet ring <b>230</b> remain intact and the first sleeve <b>211</b> does not move axially downward. Additionally, the collet head <b>234</b> of the first collet ring <b>230</b> remains engaged with the groove <b>240</b> of the body <b>220</b> of the follow wiper <b>204</b>, thereby preventing the lead wiper <b>202</b> from being released. As shown in <figref idref="DRAWINGS">FIG. 3</figref>, because the sleeve <b>215</b> of the follow wiper <b>204</b> initially abuts the upper surface of the collet head <b>234</b>, and because the collet head <b>234</b> remains fully engaged with the body <b>220</b> of the follow wiper <b>204</b>, the sleeve <b>215</b> is prevented from moving axially downward. Because the sleeve <b>215</b> is prevented from moving axially downward, the collet head <b>252</b> of the second collet ring <b>251</b> remains engaged with the body <b>220</b> of the follow wiper <b>204</b>, thereby preventing the follow wiper <b>204</b> from decoupling from the running tool <b>244</b>. In this embodiment, another downhole tool, for example a fishing tool, may be run inside the running tool <b>244</b> and latched onto the second PDP <b>270</b> to retrieve the second PDP <b>270</b> from the dual plug system <b>200</b>. Subsequently, the first PDP <b>258</b> (<figref idref="DRAWINGS">FIG. 2A</figref>) may be run downhole to decouple the lead wiper <b>202</b> from the follow wiper <b>204</b>, as described in detail above with respect to <figref idref="DRAWINGS">FIG. 2</figref>. Alternatively, the entire dual plug system <b>200</b> may be removed from the well and the second PDP <b>270</b> removed from the dual plug system <b>200</b> at the surface. The dual plug system <b>200</b> may then be run back into the well and used to cementer the liner (not shown) as described above with reference to <figref idref="DRAWINGS">FIG. 2</figref>.

Referring now to <figref idref="DRAWINGS">FIG. 5</figref>, a landing collar <b>690</b> disposed in a housing <b>691</b> at a lower end of a liner (not independently illustrated) is shown. The landing collar <b>690</b> is coupled to the housing <b>691</b> by at least one latching mechanism <b>692</b>. The latching mechanism <b>692</b> may be any device used for securing a tubular body within a housing known in the art, for example, locking dogs, ratchet split rings, anchoring devices, etc. One or more seals <b>685</b> may be disposed around the landing collar <b>690</b> and configured to seal between the landing collar <b>690</b> and the housing <b>691</b>. The landing collar <b>690</b> may include one or more tubular bodies <b>693</b> having a central bore <b>694</b> therethrough. The landing collar <b>690</b> includes at least one upper radial port <b>695</b> disposed proximate the upper end of the landing collar <b>690</b> and at least one lower radial port <b>696</b> disposed proximate a lower end of the landing collar <b>690</b>. The landing collar <b>690</b> is configured to receive the lead wiper <b>202</b> after it has been released from the dual plug system <b>200</b> (<figref idref="DRAWINGS">FIG. 2A</figref>) at the top of the liner.

When the lead wiper <b>202</b> is decoupled from the dual plug system <b>200</b> (<figref idref="DRAWINGS">FIG. 2A</figref>), as described above, the fluid pressure of the volume of cement behind the lead wiper <b>202</b> moves the lead wiper <b>202</b> axially downward to the lower end of the liner and seats the lead wiper <b>202</b> in the landing collar <b>290</b>. The threaded outer surface of the snap ring <b>219</b> disposed around the lead wiper <b>202</b> engages a corresponding threaded surface <b>697</b> of the landing collar <b>690</b> to secure the lead wiper <b>202</b> in the landing collar <b>690</b>. In one embodiment, the threaded outer surface of the snap ring <b>219</b> and the corresponding threaded surface <b>697</b> of the landing collar <b>690</b> may be ratchet threads, so as to prevent the lead wiper <b>202</b> from moving axially upward when engaged. As shown, when the lead wiper <b>202</b> moves into an upper end of the tubular body <b>693</b> of the landing collar <b>690</b>, the at least one wiping fin <b>206</b><i>a </i>is flexed or compressed within the tubular body <b>693</b>. As shown, at least a portion of an outside diameter of the landing collar <b>690</b> is less than the inside diameter of the liner, thereby providing an annulus <b>698</b>. As shown, the annulus <b>698</b> may be disposed between first latching mechanism <b>692</b><i>a </i>and second latching mechanism <b>692</b><i>b</i>. Additionally, the at least one upper radial port <b>695</b> of the landing collar <b>690</b> radially aligns with the annulus <b>698</b>.

Once the lead wiper <b>202</b> is seated and engaged within the landing collar <b>690</b>, cement may flow around the lead wiper to cement the outside diameter of the liner in place. The cement flows around the lead wiper <b>202</b> as indicated by arrow <b>699</b> and as described below. When the lead wiper <b>202</b> seats within the landing collar <b>690</b>, the lead wiper <b>202</b> is disposed axially above the at least one lower radial port <b>696</b> and the compressed wiping fins <b>206</b><i>a </i>are disposed axially below the at least one upper radial port <b>695</b>. Specifically, the volume of cement behind the lead wiper <b>202</b> flows from behind the compressed wiping fins <b>206</b><i>a </i>through the at least one upper radial port <b>695</b> into the annulus <b>698</b>. The cement then flows axially downward in the annulus <b>698</b> and through axial openings <b>655</b> of the first latching mechanism <b>692</b><i>a</i>. The cement may then flow radially inward through the at least one lower radial port <b>696</b> back into the bore <b>694</b> of the landing collar <b>690</b>. The landing collar thereby provides a bypass assembly in which the cement may flow around the lead collar <b>202</b> seated within the landing collar <b>690</b>. The cement may then be pumped upward between the liner and the formation (not shown) or other tubular (not shown) and allowed to cure.

Referring to <figref idref="DRAWINGS">FIG. 6</figref>, once the volume of cement has been pumped around the lead wiper <b>202</b> seated within the landing collar <b>690</b>, the follow wiper <b>204</b> lands within the upper end of the landing collar <b>690</b> above the lead wiper <b>202</b>. The snap ring <b>221</b> disposed around the follow wiper <b>204</b> proximate the landing nose <b>222</b> engages an inside surface of the upper end of the landing collar <b>690</b>. As shown, the snap ring <b>221</b> may include a threaded outer surface configured to engage a corresponding threaded surface <b>657</b> of the landing collar <b>690</b> to secure the follow wiper <b>204</b> in the landing collar <b>690</b>. In one embodiment, the threaded outer surface of the snap ring <b>221</b> and the corresponding threaded surface <b>657</b> of the landing collar <b>690</b> may be ratchet threads, so as to prevent the follow wiper <b>204</b> from moving axially upward when engaged. The latched follow wiper <b>204</b> seals the bore <b>694</b> of the landing collar <b>690</b> to prevent the cement from re-entering the drill string (not shown).

Referring now to <figref idref="DRAWINGS">FIG. 7A</figref>, a dual wiper plug system <b>300</b> in accordance with embodiments of the present disclosure. Dual wiper plug system <b>300</b> includes a lead wiper <b>302</b> and a follow wiper <b>304</b>. Each of the lead wiper <b>302</b> and the follow wiper <b>304</b> include one or more wiping fins <b>306</b> disposed circumferentially around the body of the wiper <b>302</b>, <b>304</b> and extending radially therefrom to contact and seal against an inner wall of a liner (not shown). The wiping fins <b>306</b> may be formed from an elastomeric material or any other know material in the art such that the wiping fins <b>306</b> are configured to flex or compress as the wiper is run through a liner or other tubular component having an inside diameter smaller than a maximum diameter of the wiping fins <b>306</b> in an expanded state.

<figref idref="DRAWINGS">FIG. 7A</figref> shows the lead wiper <b>302</b> coupled to the follow wiper <b>304</b> and the follow wiper coupled to a running tool <b>344</b> in a run-in position. The lead wiper <b>302</b> includes a tubular body <b>308</b> and a nose <b>310</b> disposed on a lower end of the body <b>308</b>. The one or more wiping fins <b>306</b><i>a </i>are coupled to the body <b>308</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. The nose <b>310</b> includes one or more ports <b>312</b> to allow fluid flow from inside the body <b>308</b> to outside the body <b>308</b>. A snap ring <b>319</b> may be disposed around the lead wiper <b>302</b> proximate the nose <b>310</b> and axially above the ports <b>312</b>. The snap ring <b>319</b> may include a threaded outer surface configured to engage a corresponding threaded surface of the landing collar (not shown) to secure the lead wiper <b>302</b> in the landing collar (not shown). In one embodiment, the threaded outer surface of the snap ring <b>319</b> and the corresponding threaded surface of the landing collar (not shown) may be ratchet threads, so as to prevent the lead wiper <b>302</b> from moving axially upward when engaged. A key <b>388</b> or bolt may be disposed in the snap ring <b>319</b> and configured to engage the snap ring <b>319</b> to the lead wiper <b>302</b> to prevent rotation of the lead wiper <b>302</b> and components of the lead wiper <b>302</b> when the lead wiper <b>302</b> is milled up after completion of the cementing process.

<figref idref="DRAWINGS">FIGS. 9A-9C</figref> show a perspective view and partial cross-section views with an open port position and a closed port position of a lower end of the lead wiper <b>302</b> with the key <b>388</b> extending through an axial opening of the snap ring <b>319</b>. The key <b>388</b> is coupled between the nose <b>310</b> and the snap ring <b>319</b> and prevents rotation of the lower end of the lead wiper <b>302</b> when the lead wiper <b>302</b> is milled up from the landing collar (not shown).

Referring back to <figref idref="DRAWINGS">FIG. 7A</figref>, the body <b>308</b> includes a bore <b>316</b> therethrough. The lead wiper <b>302</b> includes at least one sleeve <b>311</b> disposed in the bore <b>316</b>. The at least one sleeve <b>311</b> includes a threaded portion <b>314</b> disposed on the inner surface of the sleeve <b>311</b>. In one embodiment, the threaded portion <b>314</b> may be a ratchet thread. In certain embodiments, the lead wiper <b>302</b> may include a first sleeve <b>311</b> and a second sleeve <b>313</b> coupled to the first sleeve <b>311</b>, wherein a threaded portion <b>314</b> may be disposed on the inner surface of one of the first sleeve <b>311</b> and the second sleeve <b>313</b>. As shown, the second sleeve <b>313</b> may be disposed axially below the first sleeve <b>311</b>. In the run-in position, the first and second sleeves <b>311</b>, <b>313</b> are positioned axially above the ports <b>312</b>, such that the ports <b>312</b> are open. In one embodiment, the threaded portion <b>314</b> may be disposed proximate the upper end of the lead wiper <b>302</b>, but in other embodiments, the threaded portion <b>314</b> may be disposed proximate the middle or lower end of the lead wiper <b>302</b>.

One or more axial slots <b>331</b> may be formed in the body <b>308</b> of the lead wiper <b>302</b> configured to engage one or more anti-rotation devices <b>333</b> coupled to the first sleeve <b>311</b>. The anti-rotation devices <b>333</b> may include a bolt or a key configured to fit within the axial slots <b>331</b> and prevent rotation of the first sleeve <b>311</b> when the lead wiper <b>302</b> and components of the lead wiper <b>302</b> are milled up after completion of the cementing process. The anti-rotation devices <b>333</b> are be configured to move axially within the one or more axial slots <b>331</b> when the first sleeve <b>311</b> shirts axially downward, but are prevented from rotating. Preventing rotation of the components of the lead wiper <b>302</b> during milling up may provide a quicker, more efficient milling process. Similarly, one or more slots <b>335</b> may be formed in the body <b>320</b> of the follow wiper <b>304</b> configured to engage one or more anti-rotation devices <b>337</b> coupled to a third sleeve <b>315</b> of the follow wiper <b>304</b>. The anti-rotation devices <b>337</b> may include a bolt or a key configured to fit within the slots <b>335</b> and prevent rotation of third sleeve <b>315</b> of the follow wiper <b>304</b>, when the follow wiper <b>304</b> and the components of the follow wiper <b>304</b> are milled up.

The follow wiper <b>304</b> includes a tubular body <b>320</b> and a landing nose <b>322</b> disposed on a lower end of the tubular body <b>320</b>. In one embodiment, a lower end of the landing nose <b>322</b> may include a plurality of castellations <b>283</b>, as shown in <figref idref="DRAWINGS">FIG. 4</figref>. The castellations <b>283</b> are configured to provide quicker and more efficient milling up of the follow wiper <b>304</b> after landing in the landing collar (not shown). As shown in <figref idref="DRAWINGS">FIG. 7A</figref>, the one or more wiping fins <b>306</b><i>b </i>are coupled to the body <b>320</b> by any means known in the art, for example, mechanical fasteners, co-molding, press fit, etc. A snap ring <b>321</b> may be disposed around the follow wiper <b>304</b> proximate the landing nose <b>322</b>. The snap ring <b>321</b> may include a threaded outer surface configured to engage a corresponding threaded surface of the landing collar (not shown) to secure the follow wiper <b>304</b> in the landing collar (not shown). In one embodiment, the threaded outer surface of the snap ring <b>321</b> and the corresponding threaded surface of the landing collar (not shown) may be ratchet threads, so as to prevent the follow wiper <b>304</b> from moving axially upward when engaged. A key <b>377</b> may be disposed in the snap ring <b>321</b> and configured to engage the snap ring <b>321</b> to the follow wiper <b>304</b> to prevent rotation of the follow wiper <b>304</b> and components of the follow wiper <b>304</b> when the follow wiper <b>304</b> is milled up after completion of the cementing process.

The body <b>320</b> of the follow wiper <b>304</b> includes a bore <b>324</b> therethrough. The follow wiper <b>204</b> includes a third sleeve <b>315</b> disposed in the bore <b>224</b>. The third sleeve <b>315</b> includes an internal shoulder <b>317</b>, such that an inside diameter of the third sleeve <b>315</b> proximate the upper end of the shoulder <b>317</b> is larger than an inside diameter of the sleeve <b>215</b> proximate the lower end of the shoulder <b>217</b>. The shoulder may be sloped or may be formed as a right angle. As shown, the lower end of the third sleeve <b>315</b> may be configured to receive the upper end of the first sleeve <b>311</b> of the lead wiper <b>302</b> within the bore <b>324</b>.

A first collet ring <b>330</b> is coupled to the upper end of the body <b>308</b> of the lead wiper <b>302</b>. The first collet ring <b>330</b> may be coupled to the body <b>320</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The first collet ring <b>330</b> includes at least one collet finger <b>332</b> extending axially upward and configured to engage the body <b>320</b> of the follow wiper <b>304</b>. One of ordinary skill in the art will appreciate that the first collet ring <b>330</b> may include a cylindrical ring having one or more collet fingers <b>332</b> extending therefrom or may include one or more collet fingers individually coupled to the lead wiper <b>302</b>. At least one shear screw <b>323</b> may be engaged with the first collet ring <b>330</b> and extend radially inward to engage a groove <b>325</b> formed in an outer surface of the first sleeve <b>311</b>.

The one or more collet fingers <b>332</b> each include a collet head <b>334</b> configured to engage an inner ring <b>375</b> coupled to the follow wiper <b>304</b>, so as to couple the lead wiper <b>302</b> to the follow wiper <b>304</b>. The collet head <b>334</b> includes an extension portion that extends radially outward from the collet finger <b>332</b>, such that the extension portion engages an upper end of the inner ring <b>375</b> of the follow wiper <b>304</b>. As shown in <figref idref="DRAWINGS">FIG. 7A</figref>, the inner ring <b>375</b> is coupled to the body <b>320</b> of the follow wiper <b>304</b> by one or more shear screws <b>373</b>. One or more seals <b>379</b> may be disposed around the inner ring <b>375</b> between the inner ring <b>375</b> and the inner surface of the body <b>320</b> of the follow wiper <b>304</b>. The shear screws <b>373</b> of the inner ring <b>375</b> have a predetermined pressure rating that is higher than the other actuation mechanisms of the dual plug wiper system <b>300</b>. Specifically, the pressure rating of the shear screws <b>373</b> of the inner ring <b>375</b> is higher than the pressure rating of the shear screws <b>325</b> coupling first collet ring <b>330</b> and the first sleeve <b>311</b> and shear screws <b>343</b> coupling a second collet ring <b>351</b> and the third sleeve <b>315</b> of the follow wiper <b>304</b>. The inner ring <b>375</b> and the at least one shear screw <b>373</b> provide a safety mechanism for releasing the lead wiper <b>302</b> and the follow wiper <b>304</b> in the event of an emergency, for example, when the lead sleeve is jammed and the pressure cannot otherwise be released. Actuation of the lead wiper <b>302</b> and follow wiper <b>304</b> in accordance with this embodiment is described in more detail below. When a predetermined pressure is applied to the tool that is greater than the predetermined pressure rating of the at least one shear screw <b>373</b>, the shear screw <b>373</b> shears and the inner ring <b>375</b> is configured to move axially downward within an axial slot <b>365</b> formed between the body <b>320</b> of the follow wiper <b>304</b> and the collet ringer <b>332</b>.

When the follow wiper <b>304</b> and the lead wiper <b>302</b> are coupled together (e.g., when the lead and follow wipers <b>302</b>, <b>304</b> are run into the hole and positioned at the top of a liner) an outer diameter of the first sleeve <b>311</b> contacts the inner surface of the collet head <b>334</b> of the at least one collet finger <b>332</b>, thereby maintaining the collet head <b>334</b> in contact with the inner surface of the follow wiper <b>304</b> body <b>320</b>. Contact between the collet head <b>334</b> and the upper surface of the inner ring <b>375</b> coupled to the follow wiper <b>304</b> body <b>320</b> maintains engagement of the lead and follow wipers <b>302</b>, <b>304</b>.

A second collet ring <b>351</b> is coupled to the lower end of the running tool <b>344</b>. The second collet ring <b>351</b> may be coupled to the running tool <b>344</b> by any means known in the art, for example, threaded connection, welding, press-fit, or mechanical fasteners, such as bolts, screws, or shear screws. The second collet ring <b>351</b> includes at least one collet finger <b>354</b> extending axially downward and configured to engage the body <b>320</b> of the follow wiper <b>304</b>. One of ordinary skill in the art will appreciate that the second collet ring <b>351</b> may include a cylindrical ring having one or more collet fingers <b>354</b> extending therefrom or may include one or more collet fingers <b>354</b> individually coupled to the running tool <b>344</b>. At least one shear screw <b>343</b> may be engaged with the second collet ring <b>351</b> and extend radially inward to engage a groove <b>345</b> formed in an outer surface of the sleeve <b>315</b>.

The one or more collet fingers <b>354</b> each include a collet head <b>352</b> configured to engage a groove <b>350</b> formed on the inner surface of the body <b>320</b>, so as to couple the follow wiper <b>304</b> to the running tool <b>344</b>. The collet head <b>352</b> includes an extension portion that extends radially outward from the collet finger <b>354</b>, such that the extension portion engages the groove <b>350</b> of the follow wiper <b>304</b> body <b>320</b> and abuts an upset <b>348</b>. The upset <b>348</b> may be formed on the inner surface of the body <b>320</b> axially above the groove <b>350</b> or the upset <b>348</b> may be formed by a secondary ring <b>353</b> coupled to the body <b>320</b> of the follow wiper <b>204</b>.

When the follow wiper <b>304</b> and the running tool <b>344</b> are coupled together (e.g., when the lead and follow wipers <b>302</b>, <b>304</b> are run into the hole and positioned at the top of a liner) an outer diameter of the sleeve <b>315</b> of the follow wiper <b>304</b> contacts the inner surface of the collet head <b>352</b> of the at least one collet finger <b>354</b>, thereby maintaining the collet head <b>252</b> in the groove <b>350</b> of the follow wiper <b>302</b> body <b>320</b>. Contact between the collet head <b>352</b> and the upset <b>348</b> of the follow wiper <b>302</b> body <b>320</b> maintains engagement of the follow wiper <b>304</b> and the running tool <b>344</b>.

To decouple the lead wiper <b>302</b> from the follow wiper <b>304</b>, a first PDP (not shown) may be released from the surface into the drill string. When the first PDP (not shown) is run downhole, the first PDP becomes engaged with the first sleeve <b>311</b> of the lead wiper <b>302</b>. In this embodiment, a split ring (not shown) of the first PDP engages the threaded portion <b>314</b> disposed on the inner surface of the sleeve <b>311</b> to secure the first PDP within the lead wiper <b>302</b> and seal the bore <b>316</b> of the lead wiper <b>302</b>. An outer surface of the split ring (not shown) may include a ratchet thread and the threaded portion <b>314</b> of the sleeve <b>311</b> may be a corresponding ratchet thread, such that engagement of the threaded portions provides locking engagement of the first PDP with the lead wiper <b>302</b> that prevents the first PDP from moving axially upward.

Referring to both <figref idref="DRAWINGS">FIGS. 7A and 7B</figref>, hydraulic pressure applied behind the first PDP <b>858</b> by the pumped volume of cement (not shown) causes the first PDP <b>358</b> to move the first sleeve <b>311</b> axially downward, shearing the shear pins <b>323</b>, until the second sleeve <b>313</b> engages or abuts an inside surface of the nose <b>310</b> of the lead wiper <b>302</b>. When the second sleeve <b>313</b> engages the nose <b>310</b>, the ports <b>312</b> are closed by the sleeve <b>313</b>. The first sleeve <b>211</b> may include a snap ring <b>387</b> disposed in a circumferential groove <b>389</b> formed in an outer surface of the first sleeve <b>311</b>. The snap ring <b>387</b> and circumferential groove <b>389</b> may be located axially below the groove <b>325</b> formed in the first sleeve <b>311</b> configured to receive at least one shear screw <b>323</b>. The snap ring <b>387</b> may be biased radially outward. In the run-in position, the snap ring <b>387</b> is compressed within the groove <b>389</b> by contact engagement with the inner surface of the first collet ring <b>330</b>. As the first sleeve <b>311</b> moves axially downward, the snap ring <b>387</b> may radially align with a groove or shoulder <b>309</b> on the inside diameter of the body <b>308</b> of the lead wiper <b>302</b>, thereby allowing the snap ring <b>387</b> to expand radially outward to secure the first sleeve <b>311</b> to the body <b>308</b>.

The first sleeve <b>311</b> also includes a groove <b>341</b> or a reduced outer diameter portion. When the tool is run-in, the groove <b>341</b> is spaced axially above the collet head <b>334</b> a distance approximately equal to the distance between a lower surface of the second sleeve <b>313</b> and the inside surface of the nose <b>310</b>. Thus, when the first sleeve <b>311</b> moves axially downward, the groove <b>341</b> moves into radial alignment with the collet head <b>334</b> of the first collet ring <b>330</b>. As the hydraulic pressure of the volume of cement is continuously applied behind the first PDP <b>358</b>, the at least one collet finger <b>332</b> may flex radially inward allowing the collet head <b>334</b> to engage the groove <b>341</b> of the first sleeve <b>311</b> and disengage from the upper end of the inner ring <b>375</b>, thereby decoupling the lead wiper <b>302</b> from the follow wiper <b>304</b>.

<figref idref="DRAWINGS">FIG. 7C</figref> show the follow wiper <b>304</b> coupled to the running tool <b>344</b> after the lead wiper <b>302</b> (<figref idref="DRAWINGS">FIG. 7B</figref>) has been decoupled from the follow wiper <b>304</b> and run downhole. Once a predetermined volume of cement has been pumped downhole for cementing a liner in place in a borehole, the follow wiper <b>304</b> may be decoupled from the running tool <b>344</b> and run downhole to remove any excess cement from the inside wall of the liner (not shown). To decouple the follow wiper <b>304</b> from the running tool <b>344</b>, a second PDP <b>370</b> may be released from the surface after the volume of cement has been pumped downhole. Drilling fluid may be pumped behind the second PDP <b>370</b> to push the second PDP <b>370</b> down hole into the bore <b>324</b> of the follow wiper <b>304</b>. A split ring <b>380</b> is disposed around the body <b>372</b> of the second PDP <b>370</b> proximate the nose portion <b>374</b>. The split ring <b>380</b> may include a latching mechanism <b>371</b>, for example a collet finger or latching dog, configured to engage a shoulder <b>317</b> of the sleeve <b>315</b> of the follow wiper <b>304</b>. The latching mechanism <b>371</b> may include an axial portion and an extension portion such that the axial portion is configured to flex radially inward as the extension portion passes through the shoulder <b>317</b> and radially outward after the extension portion has passed through the shoulder <b>317</b>. The extension portion may then be engaged with the shoulder <b>317</b> such that the second PDP <b>370</b> may not move axially upward. In other embodiments, an outer surface of the split ring <b>380</b> may include a threaded portion. In one embodiment, the outer surface of the split ring <b>380</b> may include a ratchet thread configured to engage a threaded portion (not shown) disposed on the inside surface of the body <b>320</b> of the follow wiper <b>304</b>.

The second PDP <b>370</b> is similar to the second PDP <b>170</b> described above with reference to <figref idref="DRAWINGS">FIG. 1</figref>. The outside diameter of the body <b>372</b> of the PDP <b>370</b> is approximately equal to or slightly less than the inside diameter of the sleeve <b>315</b>. When the second PDP <b>370</b> is run downhole, the second PDP <b>370</b> engages the shoulder <b>317</b> of the sleeve <b>315</b>, thereby sealing the bore <b>324</b> of the follow wiper <b>304</b>.

Referring to both <figref idref="DRAWINGS">FIGS. 7A and 7C</figref>, hydraulic pressure applied behind the engaged second PDP <b>370</b> by the pumped drill fluid (not shown) causes the second PDP <b>370</b> to move the sleeve <b>315</b> axially downward. As the sleeve <b>315</b> moves, the shear screws <b>343</b> are sheared. The sleeve <b>315</b> includes a groove <b>381</b> or a reduced outer diameter portion. When the tool is run-in, the groove <b>381</b> is spaced axially above the collet head <b>352</b>. When the sleeve <b>315</b> moves axially downward, the groove <b>381</b> moves into radial alignment with the collet head <b>352</b> of the second collet ring <b>351</b>. As the hydraulic pressure of the volume of drill fluid is continuously applied behind the second PDP <b>370</b>, the at least one collet finger <b>354</b> may flex radially inward allowing the collet head <b>352</b> to engage the groove <b>381</b> of the sleeve <b>315</b> and disengage from the groove <b>350</b> and the upset <b>348</b> of the follow wiper <b>304</b> body <b>320</b>, thereby decoupling the follow wiper <b>304</b> from the running tool <b>344</b>.

In the event that the second PDP <b>370</b> (<figref idref="DRAWINGS">FIG. 7C</figref>) is mistakenly dropped into the well before the first PDP <b>358</b> (<figref idref="DRAWINGS">FIG. 7B</figref>), the dual plug system <b>300</b> disclosed herein is configured to prevent premature decoupling of the follow wiper <b>304</b> from the running tool <b>344</b> if the lead wiper <b>302</b> is still coupled to the follow wiper <b>304</b>. That is, the follow wiper <b>304</b> is prevented from decoupling from the dual plug system <b>300</b> if the lead wiper <b>302</b> has not yet been decoupled from the dual plug system <b>300</b>.

As shown in <figref idref="DRAWINGS">FIG. 8</figref>, where like reference characters represent like parts, in the event that the second PDP <b>370</b> is mistakenly dropped before the first PDP <b>358</b> (<figref idref="DRAWINGS">FIG. 7B</figref>), the first PDP <b>370</b> runs into the sleeve <b>315</b> of the follow wiper <b>304</b> until the outer diameter of the PDP <b>370</b> contacts the internal shoulder <b>317</b> of the follow wiper <b>304</b>. Because the lead wiper <b>302</b> is still coupled to the follow wiper <b>304</b>, the upper surface of the first sleeve <b>311</b> of the lead wiper <b>302</b> abuts a lower surface of the shoulder <b>317</b> of the follow wiper <b>304</b> sleeve <b>315</b>. As such, the latching mechanism <b>371</b> of the split ring <b>380</b> of the second PDP <b>370</b> does not fully engage the internal shoulder <b>317</b> of the sleeve <b>315</b>. The internal shoulder <b>317</b> provides a load bearing surface on the sleeve <b>315</b> of the follow wiper <b>304</b> as pressure is applied from above the second PDP <b>370</b>, thereby preventing pressure from being applied to the first sleeve <b>311</b> of the lead wiper <b>302</b>. Because pressure is not applied to the first sleeve <b>311</b> of the lead wiper <b>302</b>, the shear screws <b>323</b> securing the first sleeve <b>311</b> to the first collet ring <b>330</b> remain intact and the first sleeve <b>311</b> does not move axially downward. Additionally, the collet head <b>334</b> of the first collet ring <b>330</b> remains engaged with the inner ring <b>375</b> of the follow wiper <b>304</b>, thereby preventing the lead wiper <b>302</b> from being released. As shown in <figref idref="DRAWINGS">FIG. 8</figref>, because the sleeve <b>315</b> of the follow wiper <b>304</b> initially abuts the upper surface of the collet head <b>334</b>, and because the collet head <b>334</b> remains fully engaged with the inner ring <b>375</b> of the follow wiper <b>304</b>, the sleeve <b>315</b> is prevented from moving axially downward. Because the sleeve <b>315</b> is prevented from moving axially downward, the collet head <b>352</b> of the second collet ring <b>351</b> remains engaged with the body <b>320</b> of the follow wiper <b>304</b>, thereby preventing the follow wiper <b>304</b> from decoupling from the running tool <b>344</b>. In this embodiment, another downhole tool, for example a fishing tool, may be run inside the running tool <b>344</b> and latched onto the second PDP <b>370</b> to retrieve the second PDP <b>370</b> from the dual plug system <b>300</b>. Subsequently, the first PDP <b>358</b> (<figref idref="DRAWINGS">FIG. 7B</figref>) may be run downhole to decouple the lead wiper <b>302</b> from the follow wiper <b>304</b>, as described in detail above with respect to <figref idref="DRAWINGS">FIG. 7</figref>. In an alternate embodiment, the entire dual plug system <b>300</b> may be removed from the well and the second PDP <b>370</b> removed from the dual plug system <b>300</b> at the surface. The dual plug system <b>300</b> may then be run back into the well and used to cementer the liner (not shown) as described above with reference to <figref idref="DRAWINGS">FIG. 7</figref>.

In yet another embodiment, the dual plug system <b>300</b> includes a safety mechanism that allows both the lead and follow wipers to be released in the event that the second PDP <b>370</b> is run downhole before the first PDP <b>358</b> (<figref idref="DRAWINGS">FIG. 7B</figref>) or if the first sleeve <b>311</b> is jammed or stuck. In such an embodiment where the drill string cannot be picked up due to the pressure differentials across the system, the pressure may be released by actuating the inner ring <b>375</b> to decouple the lead wiper <b>302</b> from the follow wiper <b>304</b> and the follow wiper <b>304</b> from the running tool <b>344</b>. Referring back to <figref idref="DRAWINGS">FIG. 7A</figref>, and as discussed above, the dual wiper plug system <b>300</b> includes at least three stages or sets of at least one shear screw coupling components of the system <b>300</b> together. A first set of shear screws <b>323</b> couples the first sleeve <b>311</b> of the lead wiper <b>302</b> and the first collet ring <b>330</b>. A second set of shear screws <b>343</b> couples the third sleeve <b>315</b> of the follow wiper <b>304</b> and the second collet ring <b>351</b>. A third set of shear screws <b>373</b> couples the inner ring <b>375</b> and the body <b>320</b> of the follow wiper <b>304</b>.

The first set of shear screws <b>343</b> is rated to withstand a first pressure, the second set of shear screws <b>343</b> is rated to withstand a second pressure, wherein the second pressure is higher than the first pressure, and the third set of shear screws <b>373</b> is rated to withstand a third pressure, wherein the third pressure is greater than each of the first and second pressures. This varying pressure rating allows the lead wiper <b>302</b> to decouple from the dual wiper plug system <b>300</b> at a lower pressure than the pressure required to decouple the follow wiper <b>304</b> from the running tool <b>344</b>. In the event that there is a problem or emergency downhole and the dual wiper plug system <b>300</b> needs to be released from the running tool <b>344</b>, the pressure inside the system <b>300</b> may be increased to a third pressure, i.e., above the pressure rating of the third set of shear screws <b>373</b> to decouple the system <b>300</b>.

If the first sleeve <b>311</b> is jammed or if the second PDP <b>370</b> is run downhole first, the pressure may be increased up past the third pressure rating, i.e., the rating of the third set of shear screws <b>373</b>. Thus, as the pressure is increased up through the second pressure rating, i.e., the rating of the second set of shear screws <b>343</b>, the second set of shear screws <b>343</b> shear. The third sleeve <b>315</b> applies a load against the collet head <b>334</b> of the lead wiper <b>302</b> and the load is transferred to the inner ring <b>375</b>, until the pressure is increased up to or above the third pressure rating, thereby shearing the third set of shear screws <b>373</b>. The distance of travel of the third sleeve <b>315</b> and the corresponding groove <b>345</b> on the third sleeve <b>315</b> once the second set of shear screws <b>343</b> shear is greater than a distance of travel of the inner ring <b>375</b> within axial slot <b>365</b>. When the third set of shear screws <b>373</b> shears, the inner ring <b>375</b> shifts axially downward and allows the lead wiper <b>302</b> to decouple from the follow wiper <b>304</b>. Once the sleeve <b>315</b> moves axially downward as a result of the inner ring <b>375</b> moving axially downward, the lead wiper <b>302</b> is decoupled from the follow wiper <b>304</b> and the follow wiper <b>304</b> decouples from the running tool <b>344</b>.

In another embodiment, as shown in <figref idref="DRAWINGS">FIGS. 14A and 14B</figref>, if the second PDP <b>370</b> is run downhole before the first PDP <b>358</b> (<figref idref="DRAWINGS">FIG. 7B</figref>) or if the first sleeve <b>311</b> is jammed or stuck, the pressure differential across the system may be released by actuating the inner ring <b>375</b> to decouple the lead wiper <b>302</b> from the follow wiper <b>304</b> and the follow wiper <b>304</b> from the running tool <b>344</b>. As discussed above, the dual wiper plug system <b>300</b> includes at least three stages or sets of at least one shear screw coupling components of the system <b>300</b> together. One or ordinary skill in the art will appreciate that a shear ring may be used instead of a shear screw without departing from embodiments disclosed herein. A first set of shear screws <b>323</b> couples the first sleeve <b>311</b> of the lead wiper <b>302</b> and the first collet ring <b>330</b>. A second set of shear screws <b>343</b> couples the third sleeve <b>315</b> of the follow wiper <b>304</b> and the second collet ring <b>351</b>. A third set of shear screws <b>373</b> couples the inner ring <b>375</b> and the body <b>320</b> of the follow wiper <b>304</b>.

In this embodiment, the shear screw <b>343</b> is provided in the second collet ring <b>351</b>, such that the upper and lower sides of the shear screw <b>343</b> are in contact with the third sleeve <b>315</b>. That is, the shear screw <b>343</b> engages the groove <b>345</b> of the third sleeve <b>315</b>, wherein the axial length of the groove <b>345</b> is approximately equal to or slightly larger than the axial width of the shear screw <b>343</b>. Accordingly, when an incorrect plug is dropped, the pressure increase due to the dropped plug loads both the second and third sets of shear screws <b>343</b>, <b>373</b> simultaneously. The addition of the ratings of the second and third sets of shear screws <b>343</b>, <b>373</b> define the pressure load at which the second and third sets of shear screws <b>343</b>, <b>373</b> will shear.

The first set of shear screws <b>343</b> is rated to withstand a first pressure, the second and third sets of shear screws <b>343</b>, <b>373</b> are rated to withstand a second pressure, wherein the second pressure is higher than the first pressure. This varying pressure rating allows the lead wiper <b>302</b> to decouple from the dual wiper plug system <b>300</b> at a lower pressure than the pressure required to decouple the follow wiper <b>304</b> from the running tool <b>344</b>. In the event that there is a problem or emergency downhole and the dual wiper plug system <b>300</b> needs to be released from the running tool <b>344</b>, the pressure inside the system <b>300</b> may be increased to a second pressure, i.e., above the pressure rating of the second and third sets of shear screws <b>343</b>, <b>373</b> to decouple the system <b>300</b>, as described above.

If the first sleeve <b>311</b> is jammed or if the second PDP <b>370</b> is run downhole first, the pressure may be increased up past the second pressure rating, i.e., the rating of the third set of shear screws <b>373</b>. Thus, as the pressure is increased, the second collet ring <b>351</b> applies a load against the second set of shear screws <b>343</b>, the third sleeve <b>315</b> applies a load against the collet head <b>334</b> of the lead wiper <b>302</b>, and the load is transferred to the inner ring <b>375</b>, until the pressure is increased up to or above the second pressure rating, thereby shearing the second and third set of shear screws <b>343</b>, <b>373</b>. When the third set of shear screws <b>373</b> shears, the inner ring <b>375</b> shifts axially downward and allows the lead wiper <b>302</b> to decouple from the follow wiper <b>304</b>. Once the sleeve <b>315</b> moves axially downward as a result of the inner ring <b>375</b> moving axially downward, the lead wiper <b>302</b> is decoupled from the follow wiper <b>304</b> and the follow wiper <b>304</b> decouples from the running tool <b>344</b>. The high pressure rating of the second and third sets of shear screws <b>343</b>, <b>373</b> provides an indication at the surface that the wrong PDP has been dropped and engaged within the dual wiper plug system <b>300</b>. Thus, the shear screw <b>373</b> provides a contingency release of the lead wiper <b>302</b> or a safety release of the dual wiper plug system <b>300</b> in the event that the wrong plug is dropped.

Referring now to <figref idref="DRAWINGS">FIGS. 10 and 11</figref>, a landing collar <b>790</b> disposed in a housing <b>791</b> coupled to a lower end of a liner (not shown) is shown. As shown, the landing collar <b>790</b> includes a first portion <b>790</b><i>a </i>for receiving a ball drop mechanism, a second portion <b>790</b><i>b </i>for receiving the lead wiper <b>302</b>, and a third portion <b>790</b><i>c </i>for receiving the follow wiper <b>304</b>. Each portion <b>790</b><i>a</i>, <b>790</b><i>b</i>, <b>790</b><i>c </i>of the landing collar <b>790</b> is coupled to the housing <b>791</b> by at least one latching mechanism <b>792</b>. The latching mechanism <b>792</b> may be any device used for securing a tubular body within a housing known in the art, for example, locking dogs, ratchet split rings, anchoring devices, etc. One or more seals <b>785</b> may be disposed around at least a portion of the landing collar <b>790</b> and configured to seal between the landing collar <b>790</b> and the housing <b>791</b>. A central bore <b>794</b> is disposed through the landing collar <b>790</b> includes.

The second portion <b>790</b><i>b </i>of the landing collar <b>790</b> includes at least one upper radial port <b>795</b> disposed proximate the upper end of the landing collar <b>790</b>. The landing collar <b>790</b> is configured to receive the lead wiper <b>302</b> after it has been released from the dual plug system <b>300</b> (<figref idref="DRAWINGS">FIG. 7A</figref>) at the top of the liner. When the lead wiper <b>302</b> is decoupled from the dual plug system <b>300</b> (<figref idref="DRAWINGS">FIG. 7A</figref>), as described above, the fluid pressure of the volume of cement behind the lead wiper <b>302</b> moves the lead wiper <b>302</b> axially downward to the lower end of the liner (not shown) and seats the lead wiper <b>302</b> in the landing collar <b>390</b>. The threaded outer surface of the snap ring <b>319</b> disposed around the lead wiper <b>302</b> engages a corresponding threaded surface <b>797</b> of the landing collar <b>790</b> to secure the lead wiper <b>302</b> in the landing collar <b>790</b>. In one embodiment, the threaded outer surface of the snap ring <b>319</b> and the corresponding threaded surface <b>797</b> of the landing collar <b>790</b> may be ratchet threads, so as to prevent the lead wiper <b>302</b> from moving axially upward when engaged. As shown, when the lead wiper <b>302</b> moves into an upper end of the landing collar <b>790</b>, the at least one wiping fin <b>306</b><i>a </i>is flexed or compressed within the second portion <b>790</b><i>b </i>of the landing collar <b>790</b>. As shown, at least a portion of an outside diameter of the landing collar <b>790</b> is less than the inside diameter of the liner <b>790</b>, thereby providing an annulus <b>798</b>. As shown, the annulus <b>798</b> may be disposed between first latching mechanism <b>792</b><i>a </i>and second latching mechanism <b>792</b><i>b</i>. Additionally, the at least one upper radial port <b>795</b> of the landing collar <b>790</b> radially aligns with the annulus <b>698</b>.

Once the lead wiper <b>302</b> is seated and engaged within the landing collar <b>790</b>, cement may flow around the lead wiper to cement the outside diameter of the liner <b>790</b> in place. The cement flows around the lead wiper <b>302</b>. When the lead wiper <b>302</b> seats within the landing collar <b>790</b>, the lead wiper <b>302</b> is disposed axially above the at first portion <b>790</b><i>a </i>of the landing collar <b>790</b> and the compressed wiping fins <b>306</b><i>a </i>are disposed axially below the at least one upper radial port <b>395</b>. Specifically, the volume of cement behind the lead wiper <b>302</b> flows from behind the compressed wiping fins <b>306</b><i>a </i>through the at least one upper radial port <b>795</b> into the annulus <b>798</b>. The cement then flows axially downward in the annulus <b>798</b> and through axial openings <b>755</b> of the first latching mechanism <b>792</b><i>a</i>. The cement may then flow radially inward back into the bore <b>794</b> of the landing collar <b>790</b>. The landing collar thereby provides a bypass assembly in which the cement may flow around the lead collar <b>302</b> seated within the landing collar <b>790</b>. The cement may then be pumped upward between the liner and the formation (not shown) or other tubular (not shown) and allowed to cure.

Once the volume of cement has been pumped around the lead wiper <b>302</b> seated within the landing collar <b>790</b>, the follow wiper <b>304</b> lands within the upper end of the third portion <b>790</b><i>c </i>of the landing collar <b>790</b> above the lead wiper <b>302</b>. The snap ring <b>321</b> disposed around the follow wiper <b>304</b> proximate the landing nose <b>322</b> engages an inside surface of the upper end of the landing collar <b>790</b>. As shown, the snap ring <b>321</b> may include a threaded outer surface configured to engage a corresponding threaded surface <b>757</b> of the landing collar <b>790</b> to secure the follow wiper <b>304</b> in the landing collar <b>790</b>. In one embodiment, the threaded outer surface of the snap ring <b>321</b> and the corresponding threaded surface <b>757</b> of the landing collar <b>790</b> may be ratchet threads, so as to prevent the follow wiper <b>304</b> from moving axially upward when engaged. The latched follow wiper <b>304</b> seals the bore <b>794</b> of the landing collar <b>790</b> to prevent the cement from re-entering the drill string (not shown).

Referring to <figref idref="DRAWINGS">FIGS. 10-12</figref> together, the latching mechanism <b>792</b> of the landing collar <b>790</b> includes a landing insert <b>796</b> and a threaded c-ring <b>793</b> configured to collapse when initially installed and expand into threaded engagement with the landing insert <b>796</b>. An outer diameter of the c-ring <b>793</b> includes a threaded portion configured to engage a threaded portion of the housing <b>791</b>. The space or gap <b>707</b> provided in the c-ring <b>793</b> allows the c-ring to compress when installed in the housing <b>791</b> of the landing collar <b>790</b> and to expand radially into engagement with the housing <b>791</b> when the landing insert <b>796</b> is inserted in the c-ring <b>793</b>. The c-ring <b>793</b> further includes at least one notch <b>703</b> formed on an outside diameter. Specifically, the at least one notch <b>703</b> is configured to allow the c-ring to be efficiently milled up when the wipers <b>302</b>, <b>304</b> are milled up from the landing collar <b>790</b>. Specifically, the mill (not shown) may have a limited diameter due to the diameter of the housing <b>791</b>. By forming notches <b>703</b> on the outside diameter of the c-ring <b>793</b>, the mill only has to drill a diameter defined by the diameter between the notches <b>703</b> until the c-ring <b>793</b> breaks up into pieces. Small pieces of the c-ring <b>793</b> during milling helps fully mill the components without spinning and allows for the small pieces to be more easily returned to the surface.

In certain applications, a single wiper plug system in accordance with embodiments disclosed herein may be used instead of a dual wiper plug system. In this embodiment, a follow wiper as described above with reference to the figures above may be run downhole on a running tool and held proximate the top of the liner. A pump down plug as described above with reference to the second PDP of the figures above may be dropped to decouple the follow wiper from the running tool.

In other embodiments, one or more wiper plugs disclosed above may be used for various applications. In one embodiment, the nose section of the lead or follow plug may be decoupled from the wiper and changed with another landing nose. The nose may be configured to seat within a specific downhole tool, such that when the wiper plug is run downhole, other downhole tools may be actuated. For example, <figref idref="DRAWINGS">FIG. 13</figref> shows a wiper plug system <b>1400</b> used as a stage cementing tool. The wiper plug system <b>1400</b> includes a lead wiper <b>1402</b> and a follow wiper <b>1404</b>. The follow wiper <b>1404</b> includes a nose <b>1422</b> that is configured to activate stage tools. Thus, a wiper plug system in accordance with embodiments disclosed herein may advantageously allow for the system to be used in various downhole operations that require the activation or deactivation of a port or system.

Advantageously, embodiments disclosed herein provide a dual wiper plug system having a lead wiper and a follow wiper that prevents premature release of the lead wiper due to, for example, impact from above. Additionally, a dual wiper plug system in accordance with embodiments disclosed herein may allow for release and proper functioning of a lead wiper if a first PDP becomes stuck in the dual wiper plug system. Further, in the event that the second PDP is dropped before the first PDP, a dual wiper plug system in accordance with embodiments disclosed herein advantageously prevents the follow wiper from releasing from the running tool before the lead wiper is released.

While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.